Synthesis and characterization of polyaromatic compounds using tri(naphthyl)indium

Article abstract of DOI:10.1021/jo800438n

(Chemical Equation Presented) A variety of polyaromatic compounds bearing 1- and 2-naphthyl groups were prepared from the reactions of corresponding halides with tri(1- and 2-naphthyl)indium in good to excellent yields. Thermal, photophysical and electrochemical behaviors of carbazoles having naphthyl groups were studied. They have shown to be promising host and hole transporting materials in organic electroluminescence due to their high thermal stability, electrochemical reversibility and wide band gap.

Full text of DOI:10.1021/jo800438n

In general, the metal-catalyzed cross-coupling reactions of
organic electrophiles with organometallics are one of the most
straightforward synthetic methods for introduction of naphthyl
groups to sp2-hybridized carbon. Recently, we reported Pd-
catalyzed cross-coupling reactions using organoindium reagents
such as allylindiums4 and allenylindiums5 and carbonylative
cross-coupling reactions of tri(organo)indiums6 and tetra(orga-
no)indates7 with a variety of electrophiles. In addition, it was
found that a variety of organoindiums could be used in Pd-
catalyzed cross-coupling reactions as nucleophiles.8 During the
course of this study, we considered the possibility of extending
Pd-catalyzed cross-coupling reactions using tri(naphthyl)indium
and tetra(naphthyl)indate to synthesis of polyaromatic com-
pounds having naphthyl groups. In continuation of our studies
directed toward the development of indium-mediated organic
reactions, we described herein efficient synthesis of polyaromatic
compounds possessing naphthyl groups with tri(naphthyl)indium
and their thermal, photophysical, and electrochemical behaviors
were examined.
Synthesis and Characterization of Polyaromatic
Compounds Using Tri(naphthyl)indium
Wonhyung Lee,† Youngjin Kang,‡ and Phil Ho Lee*,†
National Research Laboratory for Catalytic Organic
Reaction, Department of Chemistry, and DiVision of Science
Education, Kangwon National UniVersity,
Chunchon 200-701, Republic of Korea
phlee@kangwon.ac.kr
ReceiVed February 24, 2008
In initial studies, we examined the stoichiometry of tri-
(1-naphthyl)indium and the catalytic activity of several pal-
ladium catalysts in the reaction of 4,4′-dihalo-1,1′-biphenyl with
tri(1-naphthyl)indium obtained from the reaction of InCl3 (1
equiv) with 1-naphthyllithium (3 equiv).9 The results are
summarized in Table 1. The desired product 1 was obtained in
24%, 41%, and 55% yields from the reaction of 4,4′-diiodo-
1,1′-biphenyl with tri(1-naphthyl)indium (0.69 equiv) in the
presence of Pd(DPEphos)Cl2, Pd(PPh3)4, and Pd(PPh3)2Cl2,
respectively (entries 2-4). Of the conditions screened, the best
results were obtained with tri(1-naphthyl)indium (1.0 equiv) in
the presence of 8 mol % of Pd(dppf)Cl2 in THF (70 °C, 7 h),
producing 4,4′-di(1-naphthyl)-1,1′-biphenyl (1) in 78% yield
(entry 7). The use of tri(1-naphthyl)indium in less than 1.0 equiv
resulted in sluggish reaction and gave lower yields. In the case
of 4,4′-dibromo-1,1′-biphenyl, coupling product 1 was produced
in 74% yield with tri(1-naphthyl)indium (1.0 equiv) in THF for
10 h (entry 11). The use of tetra(1-naphthyl)indate gave the
desired product 1 in 60% yield (entry 12).
A variety of polyaromatic compounds bearing 1- and 2-naphthyl
groups were prepared from the reactions of corresponding
halides with tri(1- and 2-naphthyl)indium in good to excellent
yields. Thermal, photophysical and electrochemical behaviors
of carbazoles having naphthyl groups were studied. They have
shown to be promising host and hole transporting materials in
organic electroluminescence due to their high thermal stability,
electrochemical reversibility and wide band gap.
In connection with synthesis of organic π-conjugated materi-
als, introduction of naphthyl groups to polyaromatic compounds
has attracted immense interest because of their potential
applications as active elements in LED and OLED.1 Polyaro-
matic compounds having naphthyl groups have formed an
important class of highly efficient and stable blue-light emitting
materials.2 It has been suggested that nonplanar derivatives of
naphthalene due to steric factors may hinder close packing and
improve the device performance. In this regard, the EL
polyaromatic compounds possessing naphthyl groups have been
designed on the basis of this principle.3 Therefore, there is still
a strong need for a preparative method of polyaromatic
compounds bearing naphthyl groups.
Under the optimized conditions, a range of polyaromatic
compounds possessing iodide and bromide reacted with tri(1-
and 2-naphthyl)indium (1-2 equiv) to produce polyaromatic
compounds having naphthyl groups in good to excellent yield
(4) (a) Lee, P. H.; Seomoon, D.; Lee, K.; Kim, H. Chem. Eur. J. 2007, 13,
5197. (b) Lee, P. H.; Seomoon, D.; Lee, K.; Kim, S.; Kim, H.; Kim, H.; Shim,
E.; Lee, M.; Lee, S.; Lim, M.; Sridhar, M. AdV. Synth. Catal. 2004, 346, 1641.
(c) Lee, K.; Lee, J.; Lee, P. H. J. Org. Chem. 2002, 67, 8265. (d) Lee, P. H.;
Sung, S.-Y.; Lee, K. Org. Lett. 2001, 3, 3201.
(5) Lee, K.; Seomoon, D.; Lee, P. H. Angew. Chem., Int. Ed. 2002, 41, 3901.
(6) Lee, P. H.; Lee, S. W.; Lee, K. Org. Lett. 2003, 5, 1103.
(7) (a) Lee, P. H.; Lee, S. W.; Seomoon, D. Org. Lett. 2003, 5, 4963. (b)
Lee, S. W.; Lee, K.; Seomoon, D.; Kim, S.; Kim, H.; Kim, H.; Shim, E.; Lee,
M.; Lee, S.; Kim, M.; Lee, P. H. J. Org. Chem. 2004, 69, 4852.
† Department of Chemistry.
‡ Division of Science Education.
(8) (a) Barbero, M.; Cadamuro, S.; Dughera, S.; Giaveno, C. Eur. J. Org.
Chem. 2006, 4884. (b) Croix, C.; Balland-Longeau, A.; Duchene, A.; Thibonnet,
J. Synth. Commun. 2006, 36, 3261. (c) Pena, M. A.; Sestelo, J. P.; Sarandeses,
L. A. Synthesis 2005, 485 and references cited therein. (d) Lehmann, U.; Awasthi,
S.; Minehan, T. Org. Lett. 2003, 5, 2405. (e) Pena, M. A.; Perez, I.; Sestelo,
J. P.; Sarandeses, L. A. Chem. Commun. 2002, 2246. (f) Takami, K.; Yorimitsu,
H.; Shinokubo, H.; Matsubara, S.; Oshima, K. Org. Lett. 2001, 3, 1997. (g)
Perez, I.; Sestelo, J. P.; Sarandeses, L. A. Org. Lett. 1999, 1, 1267.
(9) (a) Corey, E. J.; Beames, D. J. J. Am. Chem. Soc. 1972, 94, 7210. (b)
Applequist, D. E.; O’Brien, D. F. J. Am. Chem. Soc. 1963, 85, 743.
(1) Wang, L.; Lin, M.-F.; Cheah, K.-W.; Tam, H.-L.; Gao, Z.-Q.; Chen, C. H.
Appl. Phys. Lett. 2007, 91, 183054.
(2) Etori, H.; Jin, X. L.; Yasuda, T.; Mataka, S.; Tsutsui, T. Synth. Met.
2006, 156, 1090.
(3) (a) Bonvallet, P. A.; Breitkreuz, C. J.; Kim, Y. S.; Todd, E. M.; Traynor,
K.; Fry, C. G.; Ediger, M. D.; McMahon, R. J. J. Org. Chem. 2007, 72, 10051.
(b) Lee, J.-H.; Ho, Y.-H.; Lin, T.-C.; Wu, C.-F. J. Electrochem. Soc. 2007, 154,
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4326 J. Org. Chem. 2008, 73, 4326–4329
10.1021/jo800438n CCC: $40.75 2008 American Chemical Society
Published on Web 04/24/2008

TABLE 1. Reaction Optimizationa
of steric repulsion between H3 (carbazole, C3′) and H8
(naphthalene). Compounds 4 and 12 emitted violet-blue light
when irradiated by UV light. The photoluminescence (PL)
emission spectra of both compounds exhibit a similar and
structureless pattern with the emission maximum at 389 nm for
4 and at 406 nm for 12. As compared to the PL quantum yield
(ΦPL ) 95%) of 9,10-diphenylanthracene (DPA), compounds
4 and 12 show values of 33% and 36%, respectively.
It is important to note that both compounds have narrow
emission bands and small fwhm (full width at half-maximum,
ca. 40 nm) values. The fwhm is one of the major issues
associated with the improvement of color purity in electrolu-
minescence (EL), since the two properties are generally re-
lated.11 Molecules having small fwhm offer high color purity
in EL. Both compounds 4 and 12 have fairly small fwhms
compared with those of carbazole derivatives.12 Based on this
observation, application of these two compounds to EL technol-
ogy would show high color purity. The small fwhm observed
for 4 and 12 is likely attributable to the rigid naphthalene moiety.
The thermal properties of 4 and 12 were investigated by
differential scanning calorimetry (DSC) and thermogravimetric
analysis (TGA). Both compounds showed only a 5% weight
loss approximately 300 °C and were stable up to their melting
points, showing no decomposition. The glass transitions of 4
and 12 occurred at 125 and 115 °C, respectively. These results
suggest that the introduction of the naphthyl group into the
carbazole unit increases thermal stability.
The two compounds showed similar electrochemical behav-
iors. Two oxidation potentials, which consist of reversible and
irreversible processes, were observed at 1.31 and 1.82 V for 4
as shown in Figure 2. However, the oxidation potentials of
compound 12 had slightly lower values than those of 4
(reversible at 1.22 V, irreversible at 1.68 V). This result can be
attributed to the extent of effective π-conjugation as supported
by their photophysical properties. The HOMO energy levels of
entry
X
R3In (equiv)
Pd cat.
time (h) yieldb (%)
1
2
3
4
5
6
7
I
I
I
I
I
I
I
0.69
0.69
0.69
0.69
0.8
Pd2dba3CHCl3/PPh3
Pd(DPEphos)Cl2
Pd(PPh3)4
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
Pd(dppf)Cl2
14
18
24
20
21
22
7
22
22
18
10
10
16c
24
41
55
53
1.0
1.0
56
78d
8
9
10
11
12f
Br
Br
Br
Br
Br
0.69
0.69
1.0
1.0
1.0
Pd(PPh3)2Cl2
Pd(dppf)Cl2
Pd(dppf)Cl2
Pd(dppf)Cl2
Pd(dppf)Cl2
24(33)e
43(35)e
62
74d
60d(25)e
a Reactions were carried out with 4,4′-dihalo-1,1′-biphenyl (0.3 mmol)
and 4 mol % of Pd catalyst in THF at 70 °C unless otherwise noted.
b Isolated yield. c 2 mol % of Pd2dba3CHCl3 and 16 mol % of PPh3 were
used. d 8 mol % of Pd catalyst was used. e 1-[4-(4′-Bromo-1,1′-biphenyl)]naph-
thalene. f Tetra(1-naphthyl)indate (0.3 mmol) was used.
(Table 2). Reaction of 9,10-dibromoanthracene with tri(naph-
thyl)indium gave the coupling products 2 (85%) and 10 (68%)
(entries 3 and 11). The present method worked equally well
with 2,7-dibromo-9,9′-dimethylfluorene to afford 3 and 11 in
73% and 79% yields (entries 4 and 12). However, reaction of
2-naphthylindium dichloride (2 equiv) with 2,7-dibromo-9,9′-
dimethylfluorene did not proceed. Treatment of 3,6-dibromo-
9-ethylcarbazole with tri(naphthyl)indium provided 4 and 12
in 73% and 83% yields, respectively (entries 5 and 13). Tri(1-
naphthyl)indium reacted with 5,5′-dibromo-2,2′-bithiophene to
furnish 5 and mono-cross-coupling product in 59% and 29%
yields (entry 6). In the case of 2-bromo-9,9′-spirobifluorene and
1-bromopyrene, the desired products 6, 7, 13, and 14 were
obtained in good to excellent yields. Exposure of 4,4′-dihalo-
1,1′-biphenyl to tri(2-naphthyl)indium gave rise to mono-cross-
coupling product 8 and 9 despite the use of excess indium
reagent (entries 9 and 10).
Organic compounds based on carbazole, such as 4,4′-
dicarbazolyl-1,1′-biphenyl (CBP), 4,4′-bis(9-carbazolyl)-2,2′-
dimethylbiphenyl (CDBP), etc., have attracted much attention
as host or emitting materials in OLEDs because they have high
triplet energy and thermal stability as well as good film-forming
ability and quantum efficiency.10 Therefore, we have investi-
gated thermal, photophysical, and electrochemical characteristics
of 4 and 12. The UV/vis absorption and photoluminescence (PL)
emission spectra of 4 and 12 in dilute CH2Cl2 solutions are
depicted in Figure 1. The thermal, photophysical, and electro-
chemical data of 4 and 12 are summarized in Table 3.
4 and 12 were calculated from the onset of oxidation potential
OX
according to the equation IP (ionization potential) ) [(EONSET
)
+ 4.4] V13 and the LUMO energy level was obtained by
substracting of the optical band gap from the IP (Table 3). The
difference of energy levels as well as oxidation potentials
between the two compounds suggests that the position of the
naphthalene substituents attached at carbazole affects the energy
levels of the entire conjugated system. The high-lying HOMO
energy levels, wide band gaps and reversible electrochemical
oxidations of 4 and 12 suggest that both compounds have
potential for host and hole transport in OLEDs.
In conclusion, a variety of polyaromatic compounds having
naphthyl groups were effectively prepared by Pd-catalyzed
cross-coupling reactions of polyaromatic halides with tri(naph-
thyl)indium in good to excellent yields. The present method
complements the existing synthetic methods due to some
advantageous properties of tri(naphthyl)indium such as avail-
ability, ease of preparation and handling, high reactivity and
selectivity, operational simplicity, and low toxicity. These merits
make tri(naphthyl)indium useful alternatives to other organo-
metallics having naphthyl group used in cross-coupling reactions
and also mark them out as promising reagents for organic
synthesis. Some of new compounds, such as 4 and 12, have
The UV/vis spectra of 4 and 12 exhibit an intense absorption
band between 250 and 400 nm (ꢀ > 90000 mol-1 dm3 cm-1),
indicating that the electronic transitions are mostly carbazole
to naphthalene π-π*. Interestingly, the maximum peak ob-
served for compound 4 exhibits a significant blue shift (λmax
)
230 nm) relative to that of 12. In addition, the UV edge in 4
appears at a higher energy than in 12, indicating that more
effective π-conjugation between carbazole and naphthalene in
12 occurs than in 4. This result can be attributed to the extent
(11) Shirota, Y.; Kageyama, H. Chem. ReV. 2007, 107, 953 and references
cited therein.
(10) (a) Shirota, Y. J. Mater. Chem. 2005, 15, 75. (b) Tokito, S.; Iijima, T.;
Suzuri, Y.; Kita, H.; Tsuzuki, T.; Sato, F. Appl. Phys. Lett. 2003, 83, 569.
(12) Liu, X.-M.; Xu, J.; Lu, X.; He, C. Org. Lett. 2005, 14, 2829.
(13) Agrawal, A. K.; Jenekhe, S. A. Chem. Mater. 1996, 8, 579.
J. Org. Chem. Vol. 73, No. 11, 2008 4327

TABLE 2. Pd-Catalyzed Cross-Coupling Reactions of Tri(naphthyl)indium with Polyaromatic Halidesa
d
e
a 8 mol % of Pd(dppf)Cl2 was used in THF at 70 °C. b Isolated yield. c 5-Bromo-5′-(1-naphthyl)-2,2′-bithiophene. X2 ) I. X2 ) Br.
TABLE 3. Thermal, Photophysical, and Electrochemical Data for
4 and 12
b
d
e
λabs (ε),a
nm
λem
nm φPL
,
Eonset
Eg
HOMO/LUMO Tg, Td
ox
opt
c
(V)
(eV)
(eV)
(°C)
4
230 (99140) 389 0.33
246 (76630)
271 (70400)
1.23
1.14
3.3
-5.63/-2.33
125
243
115
308
297 (67140)
12 229 (59340) 406 0.36
262 (75580)
3.2
-5.54/-2.34
280 (65080)
305 (50750)
339 (20650)
a Measured in dilute CH2Cl2 solution. b Excited at 290-305 nm. c PL
quantum yields were obtained by comparison to 9,10-diphenylanthracene
d
(0.95) as a reference. Eox (onset): onset oxidation potential. Potentials
versus Ag/AgCl, working electrode Pt, 0.1 M n-Bu4NPF6-CH2Cl2, scan
rate 100 mV s-1 e Obtained from DSC measurements on the first
.
FIGURE 1. Absorption and emission spectra of 4 (solid line) and 12
(dashed line) in CH2Cl2 at 25 °C.
heating cycle with a heating rate of 10 °C/min under N2. Td was defined
as 5% weight loss.
been demonstrated to be potential promising host and hole
transporting materials in organic electroluminescence due to
their high thermal stability, electrochemical reversibility and
wide band gap. Further investigation on electroluminescent
characteristics of these molecules is in progress.
monaphthalene (0.126 mL, 0.9 mmol) by treatment with t-BuLi
(1.8 mmol, 1.7 M in pentane) at -78 °C for 15 min followed by
warming to room temperature. This compound was used im-
mediately for the preparation of the corresponding tri(1-naphth-
yl)indium. To a solution of InCl3 (66.4 mg, 0.3 mmol) in THF (2
mL) at -78 °C was added 1-naphthyllithium (0.9 mmol, 0.45 M
in Et2O) under a nitrogen atmosphere, and the mixture was stirred
for 30 min. After the cooling bath was removed, the reaction
Experimental Section
Preparation of 4,4′-Bis(1-naphthyl)-1,1′-biphenyl (1) Using Tri-
(1-naphthyl)indium. 1-Naphthyllithium was prepared from 1-bro-
4328 J. Org. Chem. Vol. 73, No. 11, 2008

δ 8.02 (d, J ) 8.2 Hz, 2H), 7.93 (d, J ) 7.7 Hz, 2H), 7.89 (d, J )
8.1 Hz, 2H), 7.82 (d, J ) 8.1 Hz, 4H), 7.63 (d, J ) 8.1 Hz, 4H),
7.58-7.46 (m, 8H); 13C NMR (100 MHz, CDCl3) δ 140.28, 140.26,
140.1, 134.3, 132.03, 131.0, 128.8, 128.2, 127.4, 126.6, 126.5,
126.3, 125.9; IR (film) 3044, 1590, 1493, 744 cm-1; HRMS (EI)
calcd for C32H22 M+ 406.1721, found 406.1723.
Preparation of 2-[4′-Iodo(1,1′-biphenyl)-4-yl]naphthalene (8)
Using Tri(2-naphthyl)indium. 2-Naphthyllithium was prepared from
2-bromonaphthalene (189.5 mg, 0.9 mmol) by treatment with t-BuLi
(1.8 mmol, 1.7 M in pentane) at -78 °C for 15 min followed by
warming to room temperature. This compound was used im-
mediately for the preparation of the corresponding tri(2-naphth-
yl)indium. To a solution of InCl3 (66.4 mg, 0.3 mmol) in THF (2
mL) at -78 °C was added 2-naphthyllithium (0.9 mmol, 0.45 M
in Et2O) under a nitrogen atmosphere, and the mixture was stirred
for 30 min. After the cooling bath was removed, the reaction
mixture was warmed to room temperature for 30 min. The solution
of tri(2-naphthyl)indium (0.3 mmol, 0.15 M in THF) was added to
a mixture of Pd(dppf)Cl2 (0.024 mmol, 17.56 mg) and 4,4′-diiodo-
1,1′-biphenyl (0.3 mmol, 121.8 mg) in THF (2 mL) under a nitrogen
atmosphere. The reaction mixture was stirred at 70 °C for 18 h
until the starting material was consumed on TLC. After being cooled
to room temperature, the reaction mixture was quenched by MeOH.
The aqueous layers were extracted with EtOAc (3 × 20 mL), and
the combined organic layers were washed with aqueous 5% HCl
(20 mL), saturated NaHCO3 (20 mL), and saturated aqueous NaCl
(20 mL), dried with MgSO4, filtered, and concentrated under
reduced pressure. The residue was purified by silica gel column
chromatography using hexane to give 8 (81.6 mg, 67%) as a white
1
solid: mp 252-254 °C; H NMR (400 MHz, CDCl3) δ 8.09 (s,
1H), 7.93 (t, J ) 9.0 Hz, 2H), 7.88 (d, J ) 6.8 Hz, 1H), 7.83-7.78
(m, 5H), 7.70-7.67 (m, 2H), 7.55-7.48 (m, 2H), 7.41 (d, J ) 8.8
Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 140.9, 140.6, 139.4, 138.3,
138.2, 134.0, 133.1, 129.3, 128.9, 128.6, 128.3, 128.1, 127.7, 126.8,
126.5, 126.2, 125.8, 93.6; IR (film) 2958, 1644, 1464, 734 cm-1
HRMS (EI) calcd for C22H15I M+ 406.0218, found 406.0221.
;
FIGURE 2. Cyclic voltammetry of 4 (top) and 12 (bottom).
mixture was warmed to room temperature for 30 min. The solution
of tri(1-naphthtyl)indium (0.3 mmol, 0.15 M in THF) was subse-
quently added to a mixture of Pd(dppf)Cl2 (0.024 mmol, 17.56 mg)
and 4,4′-diiodo-1,1′-biphenyl (0.3 mmol, 121.8 mg) in THF (2 mL)
under a nitrogen atmosphere. The reaction mixture was stirred at
70 °C for 7 h until the starting material was consumed on TLC.
After being cooled to room temperature, the reaction mixture was
quenched by MeOH. The aqueous layer was extracted with EtOAc
(3 × 20 mL), and the combined organic layers were sequentially
washed with aqueous 5% HCl (20 mL), saturated NaHCO3 (20 mL),
and saturated aqueous NaCl (20 mL), dried with MgSO4, filtered,
and concentrated under reduced pressure. The residue was purified
by silica gel column chromatography using hexane to give 1 (95.1
mg, 78%) as a white solid: mp 179 °C; 1H NMR (400 MHz, CDCl3)
Acknowledgment. This work was supported by KOSEF
through the National Research Lab. Program funded by the
Ministry of Science and Technology (No. M10600000203-
06J0000-20310). The NMR data were obtained from the central
instrumental facility in Kangwon National University. Dr. Sung
Hong Kim at the KBSI (Daegu) is thanked for obtaining the
MS data.
Supporting Information Available: Spectral data of all new
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
JO800438N
J. Org. Chem. Vol. 73, No. 11, 2008 4329